1. Field of the Invention
The present invention relates to a computer tomography apparatus using X-rays (X-ray CT apparatus) and a computer tomography method. More particularly, the present invention relates to an X-ray cone beam CT apparatus.
2. Description of the Related Art
An X-ray CT apparatus generally applies X-rays to a target object to be imaged while rotating the target object around an axis orthogonal to an X-ray optical axis between an X-ray source and an X-ray detector, and collects fluoroscopic images from every direction of 360 degrees. Reconstruction processing is performed for collected data, whereby an X-ray tomogram is provided.
An ordinary X-ray CT apparatus stores fluoroscopic image data of each of lines (each of slices) spread one-dimensionally from the X-ray source as the collected data and calculates the X-ray tomograms of the slices from the data.
In contrast, in a technique called cone beam CT (simply, cone CT), an X-ray detector having a two-dimensional effective field of view is used. Such an X-ray cone beam CT apparatus applies a cone-like X-ray beam to a target object to be examined while rotating the target object around the axis orthogonal to the X-ray optical axis of the X-ray source to obtain two-dimensional fluoroscopic images. The two-dimensional fluoroscopic images are collected at a time, whereby X-ray tomograms of multiple slices can be provided.
In the cone CT, the data provided by one imaging is increased drastically as compared with the ordinary CT in the related art. Thus, a time required for collecting the three-dimensional data of the target object can be shortened drastically as compared with the ordinary CT in the related art. However, to provide a high-resolution tomogram in a small region regardless of the ordinary CT or the cone CT, SOD (Source to Object Distance) of a distance from the X-ray source to a rotation axis center of the target object and SID (Source to Image Distance) of a distance from the X-ray source to the X-ray detector need to be adjusted for raising an imaging magnification of the fluoroscopic image. However, as the image magnification is thus raised, the field of view of the cone beam is reduced and only a small region tomogram can be provided. Therefore, it is difficult to obtain three-dimensional data of a comparatively large target object in a high resolution.
It is an object of the invention to provide a computer tomography apparatus and method that can easily collect high-resolution three-dimensional data over a wide region.
In order to accomplish the object above, the following means are adopted. According to the present invention, there is provided a computer tomography apparatus comprising: an X-ray source for applying a cone-like X-ray beam to a target object to be examined; a two-dimensional X-ray detector being disposed on an X-ray optical axis of the X-ray source so as to be opposed to the X-ray source, for obtaining X-ray fluoroscopic data of the target object; a turn table being disposed between the X-ray source and the two-dimensional X-ray detector, for mounting the target object thereon and rotating the target object around an axis orthogonal to the X-ray optical axis; a data processing section for reconstructing a plurality of tomograms of the target object cut on a plane orthogonal to a rotation axis of the turn table; a number-of-imaging-times setting section for setting the number of imaging times; and a move mechanism for moving the turn table in a rotation axis direction of the turn table by an effective view field of the two-dimensional X-ray detector each time an imaging is executed until the number of imaging times reaches the setup number of imaging times. Further, the above-mentioned computer tomography apparatus may comprises a direction setting section for setting a direction when the turn table is moved in the rotation axis direction thereof, wherein the move mechanism moves the turn table in the setup direction set by the direction setting section.
In the above-mentioned computer tomography apparatus, it is preferable that the data processing section concatenates the plurality of tomograms reconstructed to obtain three-dimensional data of the target object.
In the invention, the number of imaging times and the direction for moving the turn table are preset. Thus, the imaging operation of collecting 360-degree X-ray fluoroscopic data while rotating the turn table and the operation of moving the turn table in the rotation axis direction by the field of view in the rotation axis direction are automatically repeated. Therefore, even if the imaging magnification is raised and the view field in the rotation axis direction of the turn table is narrowed, fluoroscopic data provided by imaging a plurality of times are concatenated, thereby expanding the substantial view field in the rotation axis direction.
That is, imaging is performed as many times as the setup number of times while the turn table is moved in the rotation axis direction by the setup field view in the rotation axis direction at a time. Thus, equivalent data to that provided by imaging in the view field being a plurality of times (as many as the setup number of times) the actual field of view in width in the rotation axis direction of the turn table can be provided by the whole imaging data. Therefore, if the substantial field view in the rotation axis direction is narrowed as imaging is conducted at a high imaging magnification to provide a high-resolution tomogram, three-dimensional data over a wide region can be provided by increasing the number of imaging times.
Further, in the invention, a plurality of tomograms every imaging time provided by reconstructing fluoroscopic data collected by imaging each time are concatenated into three-dimensional data of the target object. Therefore, the provided three-dimensional data becomes high-resolution data having a wide field of view, and, for example, high-resolution three-dimensional data of a target object to be examined which is long in one direction, such as a bar-like or columnar target object, can be provided easily.